The age of 2.4 GHz radio systems is here, but how 2.4 GHz friendly is your plane?

Gliders, especially thermal duration gliders, are often flown at great distances. Can the new 2.4 GHz systems handle that range? Most of the makers are releasing "full range" receivers as well as micro receivers that seem to have shorter ranges so the opportunity to use 2.4 GHz systems in sailplanes is there.

CARBON FIBER FUSELAGE CONCERNS

However, from what I read, the 2.4 GHz systems are more sensitive to carbon fiber in the fuselage than 72 MHz systems. As I understand it, these shorter wave lengths can be more easily blocked by high carbon content in the fuselage. That doesn't mean that, if some carbon is used for spot reinforcement that your can't use 2.4 GHz. It means that an all carbon fuselage might not be very 2.4 GHz friendly, thus reducing your reliable range.

Time will tell if the radio makers can make this new technology more carbon friendly, but you might want take this into account when you look to buy your next plane. Wood, foam, most plastics, kevlar and fiberglass seem to be 2.4 GHz transparent, or nearly so.

I have discussed this with a few people and it seems that high carbon content in sailplane fuselages is not really necessary. This seems to be more of a "cool" factor than a real structural imperative. Of the composite materials, fiberglass or fiberglass/Kevlar is said to be able to be build just as strong, comparably light and is very friendly to these new radio systems.

CARBON WINGS SEEM TO BE OK

There is no clear indication yet, from what I have read, that high carbon content in the wings is much of an issue. If the receiver is placed well forward, out of the shadow of the wing, there should be little problem. For thermal duration sailplanes we are normally looking up at the plane so it is the fuselage that we have to see through, not the wing. On slope planes, even if you are in a deeply banked turn, if the receiver is in the forward part of the fuse, you should be fine. And, slope planes are often flown much closer than thermal planes so the stronger signal might more easily overcome any momentary blanking effect of a carbon wing.

All of these systems seem to have failsafe features that can be set to predetermined positions, or will default to last position if there is a momentary loss of signal. In most cases a sub second blanking might not even be noticeable in all but the most extreme situation, such as pylon racing or dynamic soaring.

If I was in the market for a new glider, I think I would want to give preference to one that would be more 2.4 GHz friendly as that is likely where I will be going in the near future.

I am not too concerned at the moment since I do not have any plans of owning a carbon plane. I think that if carbon fuselages become an issue, someone will create a work around such as routing the antenna out the fuse. Your point is valid but it seems that whenever a new technology comes about, there are many improvements over the old technology but still some new issues come up that have to be dealt with. There is no perfect radio system and likey will never be.

Should you buy a carbon plane? I would not let this stop you. Make sure you do the proper testing on the ground per the mfg specs. Also, you may want to fail safe the plane in the spin position. This should unshadow the antenna at some point.

I mounted the servo with a highly visible long "servo arm" made from yellow corplast so I could see it easily as I paced off the distance. The servo wire was fished through a wing root hole so I could leave the servo mounted outside the fuse for the tests that were "out" vs "in" concerning the fuselage.

The 3 receivers were bound to 3 different models in the TX, and I taped them to the box "test stand" as shown. They're off the ground about 1 foot which is typical for a Gas/glo fuel installation when doing range checks. This may differ from the "typical" sailplane range check, but all RX's were at the same height for the checks.

When determining the acceptable range, the TX "bind" button was pressed and held in during the entire range check. To verify control integrity, I oriented the TX antenna in various positions when testing "good" vs "no good", and always declared "good" when ALL TX antenna orientations were acceptable. I found that 2 paces was often the repeatable resolution in distance to re-acqure a control integrity condition once lost (ie: "no good", step 2 paces closer, declare "good", then back up 2 paces again to verify "no good").

Note the AR6000 displays a superior range check than the AR6100 in all cases. My guess this is due to the longer antenna wires of the AR6000.

You can see there =IS= a drastic attenuation due to the carbon fuselage. I consider the Cappuccino to be a typical carbon layup. The moral of the story is to be sure to range check your own installation. The accepted wisdom seems to be "30 paces is acceptable" and that is almost within spec for the AR7000 inside a carbon fuselage. It would be nice if the folks at Spektrum offered a remote antenna option on a new sailplane receiver. I didn't see this offered on the new AR9000.

I hypothesize that one may poke 2 holes in a carbon fuse to route the (longer) AR6000 antennae outside the fuselage, and obtain a superior range check than a fully enclosed AR7000. I did not verify this (yet). I consider the AR7000 antenna too short to attempt this.

Does anyone know if it would be possible to lengthen the antennae of ANY of these receivers to acquire better range -- especially for sailplane use?

The Fuselage is Carbon with some kevlar and some glass. The canopy is carbon/glass.

The "inside" tests were all conducted with the hatch on and the antenna completely enclosed. I attempted to orient the 7000 RX antannae orthogonally as desired, but cannot verify completely because when I pushed the components down towards the tail I'm not sure the final orientation. There isn't a lot of room to freely choose this, and final tests would need to accommodate a ballast system which will likely block the signal further, so I consider this a random yet still a best case scenario. The only metal objects at the moment in the fuselage are two wire push rods which extend from nose to tail.

When connection is lost, the servo always held it's "last good" position -- much like a PCM system does. It was very easy to see and repeat to verify the exact range check distance within a 2 pace (~6 feet) tolerance.

I consider the "control test" to be the "outside" values which is a good baseline which anyone can repeat. I showed the orientation and position of all outside antenna arrangements so that is well documented. If I did another "inside" test, it would be subject to fuselage construction and installation which likely won't match what someone else will try to duplicate.

It's fairly well known that fiberglass does NOT attenuate radio waves anywhere near as badly as carbon, so I don't consider that an issue. What is an issue is the relative placement of the spektrum components in relation to ballast / control rods and other electronics which is likely to vary widely among installations.

This test was simply to show the relative ranges among the currently available receivers, and how much each suffered from a "best case" typical carbon fuselage internal installation. It shows the need for a remote antenna if "full range" (as compared to the baseline "outside value") is desired for sailplane use.

When it comes to sailplanes I am still sitting on the fence. Don`t think I would get into 2,4 for some years yet. At least not before I get a module for one of my MPX Profi-radioes!

What I "dream of" for 2,4-systems: I hope the manufactorers will come up with 2,4-receivers which do not have their antennas connected directly to the receivers... What I hope for is receivers which have SMA- or SMB-connectors instead. Then we can run a lenght of thin coax-cables from the receiver to antennaes which can be mounted outside the fuselage! This will solve all the problems I think. A small whip behind the canopy, and another sideways mounted under the wing.

I think I will be in 2.4 by next season. Any future sailplanes I buy will be 2.4 friendly or I won't buy them. But since the fleet is pretty full right now, that is not going to be an issue for a long time.

"It's fairly well known that fiberglass does NOT attenuate radio waves anywhere near as badly as carbon, so I don't consider that an issue. What is an issue is the relative placement of the spektrum components in relation to ballast / control rods and other electronics which is likely to vary widely among installations. "

I generally agree with this above statement. Since 2.4 ghz is so new, it would be good to see a test of 2.4 reception in a fiberglass box to compare it to carbon. Some wavelengths are known for penetrating materials better than others. The above results provide an anwer to the question "How is reception of 2.4 in semi carbon enclosuer compared to no enclosure". Is it fair to say that fiberglass is equal to no enclosure? Can you point to any research that validates this? The answer to that question may also change depending on the frequency used. Maybe 72 mhz penetrates glass as if nothing was there at all. To tell you the truth, I have no idea myself.

It is sort of like cell phones. Some frequencies and technologies are know for working better inside of buildings, some do not. There are a couple of other questions that need to be answered for complete analysis. As you said before, every one has a different plane and materials that it is made of. With different materials tested, we can get closer to understanding the consequence of each type of construction as it works with different RF technologies. I would even be interested in seeing how wood might block 2.4 ghz compared to no enclosure.

IF they do come out with some sort of remote antenna system, that should resolve most carbon fuse issues.

Well, I've been using 72 MHz systems in full glass, or glass/kevlar fuselages for years internally with no issues at all. So =I= consider it a non-issue as do most of my peers.

But you do have a point rscarawa, and I'll repeat the test in a Baudis Trinity fuselage(mostly glass) tomorrow. I'll also try to put a 72 MHz system inside and outside the Capp fuselage just to round things out.

I'm not going to use that 7000 RX inside the Cap fuselage. It just seems too much of an attenuation to be safe to me. 26 paces isn't what the manual recommends (30 paces) either, and I like this plane too much to be gambling with the range.

I now hope to put that AR 7000 into the Trinity, and a 72 MHz rx into the Capp routing the antenna along the bottom outside the fuselage unless for some reason tomorrow's range check surprises me.

Quote:

ORIGINAL: rscarawa

"It's fairly well known that fiberglass does NOT attenuate radio waves anywhere near as badly as carbon, so I don't consider that an issue. What is an issue is the relative placement of the spektrum components in relation to ballast / control rods and other electronics which is likely to vary widely among installations. "

I generally agree with this above statement. Since 2.4 ghz is so new, it would be good to see a test of 2.4 reception in a fiberglass box to compare it to carbon. Some wavelengths are known for penetrating materials better than others. The above results provide an anwer to the question "How is reception of 2.4 in semi carbon enclosuer compared to no enclosure". Is it fair to say that fiberglass is equal to no enclosure? Can you point to any research that validates this? The answer to that question may also change depending on the frequency used. Maybe 72 mhz penetrates glass as if nothing was there at all. To tell you the truth, I have no idea myself.

It is sort of like cell phones. Some frequencies and technologies are know for working better inside of buildings, some do not. There are a couple of other questions that need to be answered for complete analysis. As you said before, every one has a different plane and materials that it is made of. With different materials tested, we can get closer to understanding the consequence of each type of construction as it works with different RF technologies. I would even be interested in seeing how wood might block 2.4 ghz compared to no enclosure.

IF they do come out with some sort of remote antenna system, that should resolve most carbon fuse issues.

I needed to go to another location for this test, as there was a baseball game happening in my previous test area. otherwise the methods are similar and photos document most of the installations as before.

I believe the trends observed are expected, except for an anomaly of the relatively poor outside performance of the AR7000. (55 paces vs the previous 80 paces in my first test last week). I don't have a good explanation for that data point, especially since both the Banana and Trinity had fairly good checks that were consistent. The Capp data point also agrees with the previous test.

The construction of each fuselage is as follows:

Banana : All glass except for very small thin reinforcements of carbon in the hatch/nose cone area. 2 Strips of carbon tow in the corners outlining the area that is opened up for battery/rx installation

Trinity: Glass Nose area except for a carbon ring in the very rear of the cone near the wing root, and some carbon in the corners in the radio bay area. More carbon than the banana, but still very large "windows" of glass only. My Trinity has full carbon cloth in the tail from the wing saddle area all the way down the tail.

Capp : Full carbon/kevlar cloth weave from nose to tail.

*Note : I did not install the 72MHz receiver internally inside the Trinity because the tail of the trinity is all carbon, and therefore would obscure most of the 72MHz antenna. This is not a fair comparison because the spektrum receivers enjoy a relatively unobstructed antenna installation in the nose.

I believe some of the variances can be explained by antenna placement due to the confines of the very small banana fuselage vs the bigger Trinity. The Trinity has a compartment that is excellent for horizontal placement of the auxiliary AR7000 RX and its antennae, while the main AR7000 can be positioned almost vertically a few inches ahead in the nose bay (the usual location for a RX). That compartment lies in front of the servos and is fully enclosed opposite top/bottom wise from the nose bay opening. While there is carbon reinforcement in these areas, it is not fully enclosed, and the relatively good range check reflects this.

Just want to echo a seriously well deserved "WELL DONE" to wind junkie for all the time it took for this sort of testing.

With the move to 2.4 Ghz we can't take anything for granted. Radio energy at that frequency doesn't behave like it does at our lower Mhz regions at all. Look at the use of coax for lower RF compared to waveguides at Ghz fregquencies for an example of this. And materials that are RF transparent to lower frequencies are not neccessarily as transparent at the higher end of the band.

I would love to see someone follow a similar test procedure with 2.4 GHz from Futaba or XPS compared to 72 MHz. If they were to follow a similar procedure we would have a growing list of comparable tests.

Oh how I wish I found this sooner!!! I set up my Omega II 2.5M with the AR 7000 as the receiver. The fuselage on that particular version is a 50/50 carbon fiber/Kevlar weave. After launch I kept the glider close to trim and test the control surface throws everything was dead on and she was tracking beutifully. I was impressed with the speed of the radio system working with standard servos operating at 6 volts. I then took her up to find some thermals I lost contact and never regained it. I had the failsafes set at neutral except for about 20% up elevator. She looped her way back to earth landing about a quarter mile away. My transmitter was still on when I walk up to the intact bird but the motor and servos were all chattering. When disconnecting the battery I noticed that the dual receivers were no longer lit. I thought I trashed the AR 7000 on impact but when I got everything back on the bench I was able to rebind the AR 7000 and everything worked. Needless to say I pulled the system and went back to SPCM. Carbon and Kevlar combined is a really tough composite but I don't think I'll ever get that lucky again. Again thanks guys, the testing confirmed my suspicions. I am also not thrilled that the receiver lost its bind to the transmitter so I am going to definitely limit their use to birds I fly close. -- Frank (1crash2many)

I had a scare this weekend when flying my Trinity. I was able to race it no problem last month because I never really flew it that far from myself.

On Saturday I flew from a local hang glider spot in a mix of thermal and slope air, and at one point lost control for about 2 seconds.

I was sitting down "indian style" and when the plane went into a slow corkscrew roll I stood up immediately and then regained control. I estimate the plane was slightly more than 1/4 mile away at the time. I landed immediately and did a range check and found I only had about 15 paces with the DX 7000.

I must have been a bit careless in the installation in the latest repack/repositioning of the radio in the Trinity since the race last month. In ballasting and tuning the CG I re-routed some wires and shifted the antenna placement to cause a definite blind spot for my installation.

If you recall, my trinity does have some carbon in the nose, although most of it is clear. The largest obstruction is the battery which in my case is right next to the main RX antenna. The remote antenna was placed underneath the vtail servos to the rear. I will obviously need to revisit that before attempting any slermal flying again.